1. Field of the Invention
The present general inventive concept relates to a fuser, an image forming apparatus, and a method to control the apparatus, and more particularly, to a fuser, an image forming apparatus, and a method by controlling the apparatus to control currents supplied to a plurality of heat sources.
2. Description of the Related Art
Image forming apparatuses such as general printers and all-in-one printers generally include a fuser to fuse a transferred image onto a print sheet.
As illustrated in FIG. 1, a feed roller 10 provided at an upstream portion of a paper conveyance path T feeds print sheets 1 one by one to be conveyed to a registration roller 20. When the registration roller 20 transfers the print sheet 1 to a fuser 30 provided at a downstream portion of the paper conveyance path T, the fuser 30 fixes an image transferred onto the print sheet 1.
The fuser 30 includes a pressure roller 31 and a heating roller 32 that are provided opposite each other to apply pressure and heat to the print sheet 1 to fuse an image to the print sheet 1. As illustrated in FIG. 2, the heating roller 32 includes a plurality of heat sources such as heat lamps LP1 and LP2 that are provided in parallel in a longitudinal direction in the heating roller 32. A halogen lamp can be used as each of the heat sources LP1 and LP2.
The image forming apparatus may use sheets of various sizes. The print sheet 1 passes through a gap between the pressure roller 31 and the heating roller 32. There is a need to control a fusing temperature based on a heated position of the respective sheet according to a size of the sheet.
As illustrated in FIG. 3, different illumination rates are set for longitudinal portions of the first and second lamps LP1 and LP2. For example when using first and second lamps LP1 and LP2 with a highest output power of 700 W, the image forming apparatus distributes 60% of the highest output power to a center portion P2 of the first lamp LP1, with which various types of sheets with different sizes are brought into contact, and distributes 20% to each of two outer portions thereof P1 and P3 with which no narrow sheets are brought into contact. Alternatively, the image forming apparatus distributes 30% of the highest output power to a center portion P2 of the second lamp LP2 and distributes 35% to each of the two outer portions thereof P1 and P3.
When the lamp is turned on, a large amount of current instantly flows to cause an instant decrease in AC input voltage. This has a negative effect on voltage supply to other electric devices that share an outlet with the image forming apparatus. For example, the instant voltage decrease causes flickering of light emitting devices such as incandescent lamps.
In one method illustrated in FIG. 4, when there is a need to use a plurality of lamps LP1 and LP2, the first lamp LP1 is first turned on and the second lamp LP2 is then turned on when a predetermined time has elapsed so that the first lamp LP1 becomes stable.
Another method is to gradually change a level and volume of current supplied to a lamp at an initial activation time of the lamp. As illustrated in FIG. 5, current waveforms C1 and C2 at a small level and with a small volume are first supplied to the lamp and current waveforms C3 and C4 at a small level and with a large volume are then supplied to the lamp.
However, the conventional image forming apparatus has the following problems. When there is a need to fuse an image using a plurality of heat sources, a long time is required for the apparatus to drive all the heat sources since the apparatus drives one of the heat sources after waiting until an other heat source becomes stable. Thus, the apparatus requires a long waiting time until a heating temperature reaches a fusing temperature to fuse an image to paper. If printing is performed on a print paper before the heating temperature reaches the fusing temperature, differences in temperatures of positions of the print paper heated by the heating roller cause uneven fusing of images throughout the print paper.
An inrush current may also occur at an initial activation time of each of the plurality of heat sources. For example, as illustrated in FIG. 4, an inrush current may occur at the time K when the first lamp is turned on and at the time N when the second lamp is turned on. The inrush current may cause flickering.